C. A. Pasternak

Protection against complement-mediated cell damage by Ca2+ and Zn2+.

Ca2+ and Zn2+ prevent antibody-dependent complement-induced permeability changes in tonsil lymphocytes and Lettre cells. Lactate dehydrogenase leaks out from Lettre cells at high complement:cell ratios, under which conditions higher concentrations of Ca2+ and Zn2+ are required for protection. Ca2+ and Zn2+ do not inhibit complement activation or C9 binding to Lettre cells, and prevent leakage through preformed lesions. It is concluded that the extent of complement-induced membrane damage depends on the concentration of extracellular Ca2+, and may be modulated by changes in extracellular Ca2+ or Zn2+.

The cell surface and growth in vitro

Publisher Summary This chapter describes the cell surface and growth in vitro. The mechanism by which cellular growth is controlled is crucial to an understanding of such biological processes as differentiation and cancer. As most cell types in an adult animal have rather low rates of proliferation, the problem has been approached in situations where growth is more rapid, for example, tissues in a developing embryo and tissue regenerating after wounding or surgical excision. Several substances are able to cause confluent cells to resume growth in vitro. Leaving aside nutrients, such as glucose or amino acids that are normally present in excess, most growth-stimulating substances have in common the fact that they are macromolecular and probably act at the cell surface. Many of the factors that control cellular growth, whether in vitro or in vivo, are at the cell surface. The advantages of studying cells in vitro has led to a wealth of experimental data on the role of the surface membrane in controlling growth of cultured cells. Before growth and cell division can resume, contacts between adjacent cells, and between cells and the substratum have to be loosened.